Field of the Invention
The present disclosure relates to a detection circuit for an electromechanical transducer that performs a reception of an acoustic wave such as an ultrasonic wave (hereinafter, which may simply be referred to as transducer or the like in some cases), and a driving method for the detection circuit, a probe, and a subject information acquiring apparatus. In the present specification, the acoustic wave includes an elastic wave such as photoacoustic wave, optical ultrasonic wave, sound wave, or ultrasonic wave, and the acoustic wave generated by light irradiation is particularly called “photoacoustic wave”. The acoustic wave transmitted from the probe among the acoustic waves may be called “ultrasonic wave”, and a wave obtained while the transmitted ultrasonic wave is reflected in the subject may particularly be called “reflected wave” in some cases. The term “ultrasonic wave” may be used to represent the acoustic wave in some cases.
Description of the Related Art
A piezoelectric element (PZT), a polymer molecule film (PolyVinylidene DiFluoride (PVDF)), or the like is used for a transmission and reception transducer for generating and detecting the ultrasonic wave. The “transmission and reception” mentioned in the present specification mean at least one of the transmission and the reception. Transducers that include a built-in preamplifier (voltage amplification circuit) are proposed to improve an S/N ratio of these transducers at the time of the ultrasonic wave detection (see Improving ultrasound imaging with integrated electronics (Ultrasonics Symposium (IUS), 2009 IEEE International): 2718-2721). In addition, a capacitive-micromachined-ultrasonic-transducer (CMUT) serving as an electrostatic capacitance type ultrasonic transducer is proposed. The CMUT is fabricated by using a micro-electro-mechanical-systems (MEMS) process in which a semiconductor processing is adapted. The CMUT includes a current-voltage conversion circuit to convert a current signal into a voltage signal at the time of the ultrasonic wave detection. FIG. 13 illustrates an arrangement in this circuit where an ultrasonic probe 100, an ultrasonic transducer 101, a detection circuit 102, a reception ultrasonic wave 201, a detection signal 202, and a detection output signal 203 are arranged.
According to the configuration in which the preamplifier or the current-voltage conversion circuit is built in the ultrasonic probe, a new problem of heat generation in the preamplifier or the current-voltage conversion circuit occurs. The probe includes a plurality of elements configured to transmit or receive the ultrasonic wave, and also a restriction exists on an upper limit of the heat amount that can be released from the probe. Therefore, a temperature of the probe as a whole is increased by the heat generation. The increase in the probe temperature leads to a problem particularly in a case where the probe is used while being contacted against a human body. In addition, a characteristic of the probe may be changed because of the temperature increase, and parts in contact with the probe may be affected in some cases.